Therapeutically difficult problems of the musculoskeletal system include spinal fusion, un-united fractures (or non-union fractures), failed arthrodeses, osteonecrosis, and chronic refractory tendonitis, decubitus ulcers and ligament, tendon injuries, osteoporosis, and Charcot foot. Such problems, especially fractures, may result from losses in bone mineral density. Osteoporosis in particular is responsible for 1.5 million fractures in the U.S. annually, especially hip, vertebral and wrist fractures. One conventional approach for treating such fractures is pharmaceutical therapy. This approach is disadvantageous because such therapy is generally expensive, and lasts for a patient's lifetime. Furthermore, such therapy may be associated with side effects which some patients may not tolerate.
Pulsed electromagnetic fields (PEMF) are low-energy, time-varying magnetic fields that are useful for treating such problems of the musculoskeletal system. For PEMF therapy, an electromagnetic transducer coil is typically placed in the vicinity of the fracture or fusion such that pulsing the electromagnetic transducer will produce an applied field that penetrates to the underlying bone.
One conventional approach is to use a flat oval-shaped transducer coil for PEMF fracture therapy. This approach is disadvantageous because the transducer coil may not cover the entire treatment area and the applied field has limited penetration. A second coil design for spinal fusion incorporated both a primary coil and a secondary coil to provide broad field coverage inside a defined treatment volume. Accordingly, providing effective PEMF fracture therapy using a flat coil design with broad field coverage and good field penetration required a new coil and drive circuit design which permits the use of only a single, more compact and energy efficient coil. This design is described in detail in U.S. Pat. No. 5,743,844, entitled High Efficiency Pulsed Electromagnetic Field (PEMF) Stimulation Therapy Method and System. 